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The SuperNova Acceleration Probe SNAP a Comprehensive Approach to the Study of Dark Energy

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Title: The SuperNova Acceleration Probe SNAP a Comprehensive Approach to the Study of Dark Energy


1
The SuperNova Acceleration Probe (SNAP) a
Comprehensive Approach to the Study of Dark
Energy
Gregory Tarlé University of Michigan DSU 2008
Cairo June 1, 2008
2
Welcome to Applied String Theory 501! (BUE,
Spring 2058)
  • We will start this course by having you do a
    simple and straightforward warm-up exercise.
  • Show that the energy contained in the 1 m3 empty
    box pictured here is 6.3 ? 10-10 J.

1 m
1 m
1 m
3
Golden Age of Cosmology
  • Weak lensing mass census
  • Large scale structure measurements
  • ?M 0.3

New Standard Cosmology 734 Dark Energy 274
Matter 0.5 Bright Stars Matter (27) 22 CDM,
4.4 Baryons, 0.3 ?s
4
A Fish Out of Water
  • Q What dominates this picture?
  • A The Water
  • The discovery of Dark Energy has highlighted our
    feeble
    understanding of the
    nature of the vacuum.
  • 20th century (Discovery of elementary particles,
    QM, SR, QFT, Renormalization Standard Model)
    ? The century of the
    elementary particle.
  • 21st century (Higgs, Inflation, Dark Energy,
    String Theory)
    ? The century of
    the vacuum.

Photo by L. Sander
5
Which Way Forward?
  • We know that Dark Energy is.
  • We now need to find out WHAT it is.

6
(No Transcript)
7
What we dont know
  • Precisely how much mass density (?M) and dark
    energy density (?DE) is there? How flat is the
    universe?
  • What is the equation of state (w p/r) of the
    universe and how has it changed over a time
    comparable to the age of the universe?

What is the dark energy? Theorists have
proposed a number of models, each with different
properties w(z) that we can measure. Each brings
a new understanding as to the nature of the
vacuum.
Lots of theories, little data!
Wouldnt it be nice if in 10 years we could say,
for example The dark energy is a dynamical
scalar field with an equation of state today of w
(z 0) ? w0 -0.82 0.05. The time variation
of the EOS is dw/dz ? w 0.29 0.11 consistent
with Supergravity inspired field theories..
8
An Extremely Demanding Measurement
  • We are looking for a signature of a revolutionary
    change in our understanding of fundamental
    physics
  • a previously unknown component that makes up
    most of the universe, or
  • General Relativity is wrong, or
  • evidence of higher dimensions, or
  • a clue to combining gravity/GR with the other
    forces/QCD or whatever
  • If we find a surprising result, will we (or you)
    believe it or will you just say that we have some
    sort of unknown systematic error?
  • To design an instrument based on extraordinary
    control of systematic errors we need to employ a
    comprehensive approach using complementary and
    cross-checking methodologies.
  • We need to use at least two of the four known
    approaches
  • Using two complementary methods is crucial to
    separate D.E. from GR physics explanations.
  • Using two cross-checking methods is rather
    minimal for a systematics check.

DETF Type Ia Supernovae
Weak Lensing BAO Clusters
9
presently the most powerful and best proven
technique.--DETF
  • With so few methods available, each one has to
    stand on its own feet as robustly as possible.
  • SNAP is designed around this principle for
  • the Type Ia Supernova method and
  • the Weak Lensing method

if systematics controlled, likely to be most
powerful individual technique. --DETF
10
Expansion History
Technique 1 Type Ia Supernovae
11
SNe Systematics Control
  • Supernova measurement sample
  • Requires 2000 well measured SNe
  • Study cosmologically significant redshift range
    up to 1.7

12
SNe Systematics Control
  • Supernova measurement sample
  • Requires 2000 well measured SNe
  • Study cosmologically significant redshift range
    up to 1.7
  • SN Lightcurve
  • Recognize differences between SNe

13
SNe Systematics Control
  • Supernova measurement sample
  • Requires 2000 well measured SNe
  • Study cosmologically significant redshift range
    up to 1.7
  • SN Lightcurve
  • Recognize differences between SNe
  • Recognize and correct for evolving dust
    extinction requires 3 colors

14
SNe Systematics Control
  • Supernova measurement sample
  • Requires 2000 well measured SNe
  • Study cosmologically significant redshift range
    up to 1.7
  • SN Lightcurve
  • Recognize differences between SNe
  • Recognize and correct for evolving dust
    extinction requires 3 colors
  • Spectrum
  • Identify SN type
  • Subclassification
  • Low resolution, R70 spectrum into NIR

15
Weak Gravitational Lensing
Technique 2 Weak Lensing
z2.0
z1.5
z1.0
z0.5
16
WL Systematics Control
  • Large number of resolution elements on the sky
  • To get sufficient quantity of resolved galaxies

Hubble Space Telescope Ultra Deep Field shows
many more small specks of light these are the
resolved galaxies that can be seen from space but
not from the ground
17
WL Systematics Control
  • Large number of resolution elements on the sky
  • To get sufficient quantity of resolved galaxies

Fraction of galaxies that can be studied from
space with SNAP is close to one.
18
WL Systematics Control
  • Large number of resolution elements on the sky
  • To get sufficient quantity of resolved galaxies
  • Measurement of the galaxy ellipticities (shear)
  • Requires space resolution
  • Demands stable optics

Space
Ground
Shear accuracy (rpsf / rgalaxy) 2
19
WL Systematics Control
  • Large number of resolution elements on the sky
  • To get sufficient quantity of resolved galaxies
  • Measurement of the galaxy ellipticities (shear)
  • Requires space resolution
  • Demands stable optics

Shear accuracy (rpsf / rgalaxy) 2
20
WL Systematics Control
  • Large number of resolution elements on the sky
  • To get sufficient quantity of resolved galaxies
  • Measurement of the galaxy ellipticities (shear)
  • Requires space resolution
  • Demands stable optics
  • Measurement of galaxy redshift
  • Needs excellent photometry, for photo-z
  • Requires NIR
  • Going to space ameliorates all these problems,
    controls systematics--and why the DETF considers
    this to be the option that guarantees results

NIR
21
SNAP A Wide-Field Space Telescope Optimized for
the Study of Dark Energy
  • SNAP concept eliminates complexity
  • Innovative telescope design does NIR imaging with
    room temperature optics

3-mirror anastigmat for large flat focal plane.
Compact, Stable
22
With very few moving parts.
SNAP concept eliminates complexity Fixed solar
panels, passive cooling,
fixed antenna eliminates major
mission risks.
radiator
Solar panel
antenna
23
A single focal plane
  • All instruments/detectors on single focal plane.
  • Vis-NIR imager (0.7 deg2 FOV, 9 fixed filters
    from 350nm to 1700nm)
  • Vis-NIR Spectrograph (R70-100)
  • Passively cooled to 140K

24
An extremely stable environment L2
L2 Orbit, puts burden in the launch vehicle and
takes it away from the spacecraft. Small fuel
required for injection, station keeping, angular
momentum.
Earth and Moon Illumination
25
The SNAP Collaboration
140 people from Lawrence Berkeley National
Lab Univ. of California Berkeley California
Inst. of Technology Fermi National Accelerator
Lab Goddard Space Flight Center Indiana
Univ. IN2P3 Paris IN2P3 Marseille Jet
Propulsion Lab Le Laboratoire d'Astrophysique de
Marseille Sonoma State Univ. of British
Columbia/Victoria Univ. of Maryland Univ. of
Michigan Univ. of Pennsylvania Univ. of
Stockholm Stanford Linear Accelerator Lab Space
Telescope Science Inst. Yale Univ.
26
New CCD technology tolerates radiation in space
SNAP
  • Traditional n-channel CCDs are sensitive to
    radiation damage due to loss of Charge Transfer
    Efficiency (CTE)
  • LBNL p-channel CCDs are 10-50x more radiation
    tolerant

27
NIR sensors now exceed original SNAP goal
SNAP
  • NIR QE was low when RD began.
  • Total Noise now well below 10 e-
  • Summed Intrapixel response lt 1
  • Largest sensor was 1k x 1k, now 2k x 2k.

28
Spectrograph
  • Developed by Marseille group
  • Visible and NIR, R 70 - 100
  • Multi-object based on image slicer (15 slices)
  • Datacube x ? y (3? ? 6? FOV) ????? can be used to
    subtract galaxy.

slice 1 slice 2 slice 3 slice 4 slice 5
29
Observation Strategy SNe (22 months)
  • Scan 7.5 deg2 with 4 day cadence for discovery
    and follow up.
  • Targeted spectrum taken near peak brightness.
  • Focal plane 90o symmetry allows quarterly
    rotation of satellite to maintain power and
    cooling.

30
Observation Strategy Weak Lensing (12
mo./36 mo. extended survey)
  • Wide field survey
  • One time visit to each 0.7 deg2 field.
  • Fill in the sky over time to 1000 4000 deg2.

31
SNAP Surveys
1000 more sq.deg / year
  • Synergy of Supernovae Weak Lensing
  • Comprehensive no external priors required!
  • Independent test of flatness to 1-2
  • Complementary (SNe WL only)
  • conservative w0 to 0.05, variation
    w? to 0.12 (with systematics) L model w0 to
    0.03 variation w? to 0.06 (with systematics)
    SUGRA model
  • Adding extended survey and better
    systematics w0 to 0.03, variation w? to
    0.06 (with systematics) L model w0 to 0.015
    variation w? to 0.03 (with systematics) SUGRA
    model

32
Conclusions
  • Understanding the nature of Dark Energy is an
    extremely demanding scientific goal that will
    require a comprehensive approach involving
    several strategies (SNe, WL, BAO, Clusters).
    All of these are systematics limited.
  • SNAP is aimed primarily at SNe and WL for which
    the most stringent control of systematic errors
    is possible in a space experiment.
  • A straightforward simple satellite can do the job
    and RD (sensors, telescope, spacecraft,
    electronics) is now complete thanks to a 5 year
    DoE sponsored RD effort.
  • The SNAP investigation will result in constraints
    on theories of Dark Energy (w0, wa) and Gravity
    (and a HUGE 9-band, high resolution deep sky
    survey.
  • SNAP is a prime candidate for the DoE and NASA
    Joint Dark Energy Mission that will be announced
    later this year.
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